I decided that, with all of the rain we've been having (AZ monsoon season) and the mud and road grime that got on it, it was time to clean'r up... It took forever and with the summer heat, the water dried up more quickly than I could wipe it off and now I have a windshield that looks like crap.

I tried vinegar and it helped a little, but it's still there and "I" notice it a lot. I used this Rain-X windshield foam stuff with the microfiber towel, and it helped a little more, but still there...

I had a horrible bout with hard water a few weeks ago, washing my truck at my buddies house. If you drank enough of this water, you would probably crap an iron bar. I ended up rewashing it at a DIY drive thru, and used the pink foaming brush thing on all the glass. Took care of it.

There are OODLES of chemicals that can remove it... what you're seeing is scale from dissolved minerals in the water...

Here's what worked for me recently on a car I was doing for a client...

I couldn't remove them by any mechanical measure and really didn't want to resort to a highly abrasive polish to knock them down... I went in and got a spray bottle of CLR (Calcium Lime Rust) remover (green bottle). I sprayed it on a shop rag and wiped down the windows.

Follow with a quality glass cleaner and, presto. DO NOT get the CLR on ANYTHING other than the glass as it's highly acidic and can cause pitting and other problems on coated surfaces.... word to the wise... use at your own risk...